Two-dimensional (2D) semiconductor materials have attracted considerable attention in the field of photocatalysis due to the high interfacial charge separation efficiency and abundant surface active sites. Herein, we have fabricated 2D/2D sheets of Ni 2 P/CdS heterostructure for photocatalytic H 2 evolution. The microscopic and photocatalytic activity results suggested that Ni 2 P nanosheets were coupled with snowflake CdS. The optimal hydrogen production rate reached 58.33 mmol h -1 g -1 (QE = 34.38%, λ = 420 nm) over 5 wt% Ni 2 P, which is equivalent to that of 1 wt% Pt/CdS. Compared with pure CdS, Ni 2 P/CdS presented lower fluorescence intensity and stronger photocurrent density, which demonstrated that the 2D/2D Ni 2 P/CdS heterojunction photocatalyst significantly improved the separation efficiency of photogenerated electrons and holes. The excellent performance of Ni 2 P/CdS clearly indicated that Ni 2 P was an excellent cocatalyst and could provide abundant active sites for hydrogen evolution.